The present invention relates to an active suspension apparatus using hydropneumatic devices for suspending a vehicle body on wheels by utilizing fluid or gas pressure.
There is a conventional damping apparatus for vehicle suspension wherein a vehicle travel speed, a relative displacement between wheels and corresponding axles, its relative velocity, and a vehicle acceleration are given as state variables so as to change damping characteristics of shock absorbers. Control conditions are limited on the basis of evaluation standards of individual state variables although travel conditions of a vehicle vary greatly, thus disabling proper control of the characteristics of damping force in accordance with states of a road surface. In particular, flexibility in control conditions is so limited as to decrease transient vibrations due to unevenness of a road surface and at the time when a vehicle rides over a bump and to improve stability and controllability of a vehicle when the vehicle detours an obstacle. As a result, satisfactory vibration and stability control of the vehicle cannot be performed, resulting in inconvenience.
In general, vehicles ride on various roads with surfaces varying from a smooth road surface to a rough road surface at a wide speed range from a high speed to a low speed. Therefore, the characteristics of damping forces in the suspension apparatus must be adjusted to satisfy possible road conditions. According to the conventional techniques, the damping forces are switched to reduce pitch/bounce motion at the time of starting and braking of the vehicle and rolling motion at the time of lane changing. In this case, optimal control is not based on the actual road state but on the level control or control for a predetermined period of time. Thus, the conventional control cannot cover all travel conditions.